The present invention relates generally to a hybrid inflatable antenna system that combines a fixed antenna with an inflatable portion.
Inflatable antennas are the focus of current space technology research because of their potential for enabling high bit rate data communication. Current inflatable antenna designs use gas inflation to deploy and form the reflector surface. The capability of the antenna depends on the success of the inflation process and the accuracy in rigidizing the reflector surface. This process can be a significant risk to the mission if there is not a backup system. Large inflatable antenna systems are often designed for xe2x80x9call-or-nothingxe2x80x9d and if they don""t work, the satellite mission can be a complete loss. For this reason, the application of inflatable antennas is presently limited mainly to missions where a very large aperture is needed to enable the mission. Examples of such missions include interstellar probes and large imaging radar satellites.
What is needed is an inflatable antenna system that can return a high bit rate from space while maintaining a mission-critical moderate bit rate backup capability in case of inflation failure.
A hybrid inflatable antenna system has been developed that avoids the aforementioned xe2x80x9call-or-nothingxe2x80x9dscenario by providing backup capability in the event of an inflation failure. The system combines a fixed radiating area with an inflatable portion to greatly increase the radiating area of the antenna system while in orbit. The fixed portion provides a xe2x80x9crisk bufferxe2x80x9din that moderate gain capability is retained in the event of an inflation failure. A fixed feed system assures operation of the smaller fixed portion of the antenna throughout the mission regardless of whether inflation of the larger portion of the antenna is successful.
In accordance with a first embodiment of the invention is a hybrid inflatable parabolic dish antenna system. The system is comprised of a fixed dish antenna portion capable of moderate bit rate data transmissions and a stowable inflatable annulus portion. The system also includes means for deploying the inflatable annulus portion thereby providing the overall hybrid dish antenna system with a larger reflective surface capable of higher bit rate data transmissions. First and second feed systems operatively illuminate the smaller fixed dish antenna portion and the larger inflated dish antenna portion, respectively.
The first feed system is fixed (non-deployed) thereby providing guaranteed operation of the smaller fixed dish portion of the antenna system. The second feed system may be either fixed or deployed for operation of the larger inflated dish portion of the antenna system. The fixed and inflated portions of the antenna system may be operated simultaneously, if desired, to provide separate apertures for uplink and downlink communications. In this configuration, a dual function capability exists whereby an uplink signal received by the smaller aperture can be used to provide pointing information for a downlink signal transmitted by the larger aperture.
The inflatable annulus is stowed compactly under the fixed dish portion to fit a variety of spacecraft and launch vehicle envelopes. Moderate gas pressure deploys the annulus which then forms a parabolic reflector surface. After inflation, the materials that comprise the annulus surface may be rigidized using temperature, ultra violet (UV), or other curing methods. For example, the present invention can be applied to a typical one (1) meter fixed dish to increase its diameter to four (4) meters or more. An inflated four (4) meter dish antenna can return a bit rate on the order of 1 Mbps from Mars using a 30 watt Ka-band power amplifier.
In accordance with a second embodiment, a hybrid inflatable antenna includes first and second feed systems. The first feed system operatively illuminates the fixed antenna portion. The second feed system includes a feed antenna and a sub-reflector. The sub-reflector reflects signals from the feed antenna onto the inflatable antenna portion. The sub-reflector is axially symmetric and its nominal shape can be elliptical or hyperbolic. In addition, its shape can be modified and optimized to correct for deformations on the inflatable antenna portion. The sub-reflector can include an array of RF reflective elements that can be remotely adjustable. Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.